❄️ Freeze warnings, ☃️ major snow, and ☔️ heavy rain. Oh my!

Another historically active weather week in Arizona.

*19 February 1874 – Reports of 4 to 6 feet of snow in Prescott.
*16-23 February 1891 – Heavy rainfall from two Pacific storms falls across nearly all of Arizona, leading to extensive flooding.
*13-25 February 1980 – A total of six storms moved from the Pacific Ocean into Arizona.
*13 February 1992 – Widespread thunderstorms and weak  tornado developed in Phoenix as well as Tempe and tornado in Apache Junction damaged numerous mobile homes.
*13 February 1995 – An (F1) tornado occurred at the General Motors Desert Proving Grounds facility. About 20 vehicles were damaged and moved around. One vehicle was lifted, moved several feet, and set down inside a roped off area containing solar exposure equipment.
*20 February 2013 – Snow levels dropped to approximately 2000 feet, and several inches of snow fell in the higher elevations east of Phoenix. The Superstitions were completely snow covered for a time. Later that afternoon, instability showers brought widespread graupel and small hail to Scottsdale, Mesa, and Gilbert. Portions of the Loop 101 and US 60 highways were completely covered with graupel during the evening rush hour.

**19-22 February 2019 – another winter storm headed our way with freeze warnings, heavy snowfall in the northern part of the state and heavy rain in the valley. Arizona has seen several storms already this year.

I thought it was warm Arizona? What’s the deal?

All this current heavy rain and snow in Arizona is brought to you by the Pineapple Express, one of the most well known atmospheric rivers.

This animation from NOAA's Earth System Research Laboratory shows an atmospheric river event in January 2017.

What is an atmospheric river? 

An atmospheric river is a narrow region in the atmosphere that is full of moisture. They originate in the tropics. The Pineapple Express originates from Hawaii building moisture and when prevailing winds cross over this vapor it brings it to the U.S. and Canadian west coast. It is simply a ‘river’ of moisture in the atmosphere.

NOAA image

Can a river in the atmosphere be as scary as it sounds? 

Although it is water vapor, not liquid, an atmospheric river can possibly be around a hundred miles wide and a few thousand miles long! The reference of a river is in fact quite accurate. They are capable of carrying more water than the Earth’s largest river, the Amazon River.

That’s a lot of water!

Oak Creek

Is the Pineapple Express always so disruptive?

No. Many other years it is much weaker and simply provides the much needed rain and snow to the western areas of the U.S. and Canada. 

When does the Pineapple Express make its way to the U.S. and Canada?

 When a cold front from the arctic sweeps up water vapor from the Hawaii area as it catches up with the warm front. This causes a narrow band of high water vapor to form in front of the cold front. Typically between November and April. 

Why is it so cold if it is coming from Hawaii?

This atmospheric river, although it comes from Hawaii, is brought over by a strong polar jet stream. Think of the ‘Polar Express’ colliding with the ‘Pineapple Express’.

For Thursday and Friday there is heavy widespread rain in the forecast for Phoenix, a significant amount of snow (measured in feet, not inches) in the northern parts of Arizona, and a snow level down to 3,000 feet! We should see a bit of snow in the mountains in the Phoenix area including black Mountain in Cave Creek which is 3,403 feet in elevation. 
With mostly sunny skies and warmer temperatures this weekend, it will be fantastic for exploring the snow covered high country. Let us do the driving and join us on a Grand Canyon or Sedona tour!
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